This display is a 3.3V display so it should be powered as such, however, the Arduino Uno does not provide 3.3V logic. I have an Arduino with a swapped voltage regulator (3.3V), but I have used 5V logic before and it still works to show something on the LCD (not recommended for extended use). For this purpose, you may connect it to the 5.0V supply.

I have never tested this before, but since 5V is outside the maximum rating, after many hours of use it could ruin the controller. The only way to test if the module is functioning is to power it up and write characters to it.

I got the arduino HelloWorld example working (but only with 4 pins, not 8-pin operation). Turns out I was getting pins 1-8 mixed up with pins 7-16.

However, the sample code you provided in the other forum thread only occasionally print the correct message, and then otherwise print gibberish. The arduino helloWorld code prints gibberish in 8-bit mode.